From 0722ab14b52ff5db103f551b50dc164ca17f7993 Mon Sep 17 00:00:00 2001
From: Grzegorz Piwowarek <gpiwowarek@gmail.com>
Date: Mon, 14 Oct 2024 09:23:10 +0200
Subject: [PATCH] Introduce dedicated SamplingGatherer (#31)

---
 README.md                                     |  2 +-
 .../pivovarit/gatherers/MoreGatherers.java    | 18 ++----------
 .../pivovarit/gatherers/SamplingGatherer.java | 29 +++++++++++++++++++
 .../{SampleTest.java => SamplingTest.java}    | 14 ++++-----
 4 files changed, 39 insertions(+), 24 deletions(-)
 create mode 100644 src/main/java/com/pivovarit/gatherers/SamplingGatherer.java
 rename src/test/java/com/pivovarit/gatherers/blackbox/{SampleTest.java => SamplingTest.java} (55%)

diff --git a/README.md b/README.md
index a94181c..0f168ec 100644
--- a/README.md
+++ b/README.md
@@ -18,7 +18,7 @@ Whenever possible, the library follows Project Reactor's naming conventions.
 
 Provided `Gatherers`:
 - `MoreGatherers.last(int)`
-- `MoreGatherers.sample(int)`
+- `MoreGatherers.sampling(int)`
 - `MoreGatherers.zip(Iterator<T2>)`
 - `MoreGatherers.zip(Iterator<T2>, BiFunction<T1,T2>)`
 - `MoreGatherers.zip(Stream<T2>)`
diff --git a/src/main/java/com/pivovarit/gatherers/MoreGatherers.java b/src/main/java/com/pivovarit/gatherers/MoreGatherers.java
index e159744..37d495f 100644
--- a/src/main/java/com/pivovarit/gatherers/MoreGatherers.java
+++ b/src/main/java/com/pivovarit/gatherers/MoreGatherers.java
@@ -9,7 +9,6 @@
 import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.stream.Gatherer;
-import java.util.stream.Gatherer.Integrator;
 import java.util.stream.Stream;
 
 import static java.util.stream.Gatherer.Integrator.ofGreedy;
@@ -24,21 +23,8 @@ private MoreGatherers() {
         return new LastGatherer<>(n);
     }
 
-    public static <T> Gatherer<T, ?, T> sample(int n) {
-        if (n <= 0) {
-            throw new IllegalArgumentException("sample size can't be lower than 1");
-        }
-        return n == 1
-          ? noop()
-          : Gatherer.ofSequential(
-          () -> new AtomicLong(),
-          Integrator.ofGreedy((state, element, downstream) -> {
-                if (state.getAndIncrement() % n == 0) {
-                    downstream.push(element);
-                }
-                return true;
-            }
-          ));
+    public static <T> Gatherer<T, ?, T> sampling(int n) {
+        return new SamplingGatherer<>(n);
     }
 
     public static <T, U> Gatherer<T, ?, T> distinctByKeepLast(Function<? super T, ? extends U> keyExtractor) {
diff --git a/src/main/java/com/pivovarit/gatherers/SamplingGatherer.java b/src/main/java/com/pivovarit/gatherers/SamplingGatherer.java
new file mode 100644
index 0000000..250cc47
--- /dev/null
+++ b/src/main/java/com/pivovarit/gatherers/SamplingGatherer.java
@@ -0,0 +1,29 @@
+package com.pivovarit.gatherers;
+
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.function.Supplier;
+import java.util.stream.Gatherer;
+
+record SamplingGatherer<T>(int n) implements Gatherer<T, AtomicLong, T> {
+
+    SamplingGatherer {
+        if (n <= 0) {
+            throw new IllegalArgumentException("sampling frequency can't be lower than 1");
+        }
+    }
+
+    @Override
+    public Supplier<AtomicLong> initializer() {
+        return AtomicLong::new;
+    }
+
+    @Override
+    public Integrator<AtomicLong, T, T> integrator() {
+        return Integrator.ofGreedy((state, element, downstream) -> {
+            if (state.getAndIncrement() % n == 0) {
+                downstream.push(element);
+            }
+            return true;
+        });
+    }
+}
diff --git a/src/test/java/com/pivovarit/gatherers/blackbox/SampleTest.java b/src/test/java/com/pivovarit/gatherers/blackbox/SamplingTest.java
similarity index 55%
rename from src/test/java/com/pivovarit/gatherers/blackbox/SampleTest.java
rename to src/test/java/com/pivovarit/gatherers/blackbox/SamplingTest.java
index 876fb0e..328286e 100644
--- a/src/test/java/com/pivovarit/gatherers/blackbox/SampleTest.java
+++ b/src/test/java/com/pivovarit/gatherers/blackbox/SamplingTest.java
@@ -4,31 +4,31 @@
 
 import java.util.stream.Stream;
 
-import static com.pivovarit.gatherers.MoreGatherers.sample;
+import static com.pivovarit.gatherers.MoreGatherers.sampling;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
-class SampleTest {
+class SamplingTest {
 
     @Test
     void shouldRejectInvalidSampleSize() {
-        assertThatThrownBy(() -> sample(0))
+        assertThatThrownBy(() -> sampling(0))
           .isInstanceOf(IllegalArgumentException.class)
-          .hasMessage("sample size can't be lower than 1");
+          .hasMessage("sampling frequency can't be lower than 1");
     }
 
     @Test
     void shouldSampleEmpty() throws Exception {
-        assertThat(Stream.empty().gather(sample(42))).isEmpty();
+        assertThat(Stream.empty().gather(sampling(42))).isEmpty();
     }
 
     @Test
     void shouldSampleEvery() {
-        assertThat(Stream.of(1,2,3).gather(sample(1))).containsExactly(1,2,3);
+        assertThat(Stream.of(1,2,3).gather(sampling(1))).containsExactly(1,2,3);
     }
 
     @Test
     void shouldSampleEveryOther() {
-        assertThat(Stream.of(1,2,3).gather(sample(2))).containsExactly(1,3);
+        assertThat(Stream.of(1,2,3).gather(sampling(2))).containsExactly(1,3);
     }
 }